Transistor components, such as e.g. power MOSFETs (metal oxide semiconductor field effect transistors) or power IGBTs (insulated gate bipolar transistors), are increasingly being used as electronic switches for switching electrical loads in automotive or industrial applications. Such components are distinguished by a low on resistance in the switched-on state, and hence by low power losses. During normal operation, i.e. in the case of a fault-free load, the voltage drop across the load path of a switched-on power transistor lies in the range of a few hundred millivolts (mV) or a few volts (V). The power transistor is designed to take up the power loss associated with such a voltage drop and the associated load current. If the voltage across the load path of the power transistor rose significantly, as would be the case for example upon the occurrence of a short circuit in the load, then the load current would also rise. During the short-circuit case, the power transistor limits the flowing load current, for which reason the majority of the supply voltage is present at the power transistor. The power loss at the component rises considerably as a result, which could lead to destruction of the component, even before a protective circuit possibly present could turn the component off.
In order to protect a power transistor against such an overload, a diode can be connected in parallel with part of its load path, as is described in Constapel et al. “Trench-IGBTs with Integrated Diverter Structures”, ISPSD 1995, pp. 201-205. The diode is connected up in such a way that it limits the voltage drop across that part of the load path with which it is connected in parallel to the value of its forward voltage, as a result of which a maximum current flowing through the component (short-circuit current) is also limited. The voltage drop across that part of the load path with which the diode is connected in parallel is in this case lower than the forward voltage of the diode during the normal operation of the power transistor, such that the diode does not influence the functioning of the power transistor in the switched-on state thereof. In order to realize such a diode, Constapel et al., loc. cit., proposed providing a p-doped region in an n-doped drift zone in an IGBT, this region being connected via a p-type base or body zone and the n-type emitter zone or source zone to a cathode electrode or source electrode. However, the provision of such a structure can lead to a reduction of the dielectric strength of the component when the component is in the off state.